1. Technical Field of the Invention
The present invention relates to a carrier conveying apparatus which is suitable for conveying carriers or the like in which, for example, substrates to be processed are accommodated and also relates to an elevating mechanism installed in the carrier conveying apparatus. In addition, the invention relates to a heat treatment installation.
2. Description of the Related Art
In general, a production process of semiconductor devices includes various steps of applying an oxidation process, diffusion process and CVD process etc. on semiconductor wafers as objects to be processed. Thus, in view of the improvement of throughput, cleanness and space-conserving etc. of these steps, a variety of processing apparatuses have been proposed [e.g. see Japanese Unexamined Patent Publication (Kokai) No.4-133422].
For example, the processing apparatus disclosed in the above publication includes a vertical heat treatment furnace arranged on a rear and upper side inside a casing of the apparatus, for heat-treating a great number of wafers at a time, using a wafer boat as a carrier for objects to be processed. On the front side of the casing, a carrier input/output port (also called an I/O port) is provided for inputting and outputting a carrier as a container for accommodating a plurality of wafers therein.
Inside the above-mentioned casing, there are provided a carrier keeping section which is positioned on an upper side of the casing close to the carrier I/O port, for keeping a plurality of carriers; a carrier set-up section and a wafer boat set-up section both of which are arranged between the carrier I/O port and the heat treatment furnace, for delivering the wafers between the carrier and the wafer boat; and a wafer conveying mechanism for delivering the wafers between the carrier set-up section and the wafer boat set-up section. Further arranged in the casing is a carrier conveying apparatus with an elevating mechanism, which carries out the delivery of carriers between the carrier I/O port and the carrier keeping section, between the carrier keeping section and the carrier set-up section or between the carrier I/O port and the carrier set-up section.
Since it is necessary that, in the carrier conveying apparatus, the elevating mechanism has a relatively large stroke of e.g. 3 m to 5 m and the difficulty that the elevating mechanism employs a ball screw, a mechanism to elevate an elevating mechanism suspended by a wire or a timing belt as a suspension member is adopted as the elevating mechanism. Despite high strength in the suspension member, it is expected that if the suspension member is broken off, then utensils might be damaged because of the drop of such a heavy elevating mechanism weighing 70 to 80 kg, for example. Therefore, the above elevating mechanism is so constructed that, when a sensor detects the cutting of the suspension member, the elevating mechanism is stopped by a brake mechanism, thereby preventing the mechanism from falling.
In the above-mentioned elevating mechanism, however, it is necessary to provide a sensor for detecting the cutting of the suspension member and a control unit with electric circuits for controlling the brake mechanism by inputting a signal from the sensor etc. Therefore, with the increase in manufacturing cost and necessity of using electricity, there is a possibility that the elevating mechanism will have a faulty operation due to misidentification by the sensor.